To all but the newest Corvette enthusiast, the name Greenwood is synonymous with '70s Corvette racing and highly tuned street cars. A recent retrospective of the Greenwood line of automobiles held at Carlisle 2004 illustrated the breadth of talent that John and Burt Greenwood brought to the Corvette hobby.
Now, Tim and Joe Greenwood, sons of John Greenwood, have set up their own business to develop and sell Corvette aerodynamic aids. The first kit to be offered is their G5 Series ground-effects package. Comprising a two-piece front splitter, side skirts, two rear valance panels, and a central tunnel, the G5 Series package is ideally suited to the C5. A choice of two rear wings and a unique three-piece windshield fairing is also offered. But there are already a lot of aero kits on the market. So what makes this one different?
The simple answer is that this kit not only looks good-it works. This is reflected in the materials used, the manner in which the pieces are fabricated, and the many special features designed to ensure consistent performance and longevity. Tellingly, many sales to date have been to replace lower-quality kits.
In terms of construction, the Greenwood kits are built using a vinylester resin and gelcoat system that are more resistant and have superior longevity compared with polyester resins. The cores of the major pieces (such as the tunnel, front splitter, and side skirts) incorporate a closed-cell foam structure that provides extra rigidity (thereby eliminating flex) with virtually no extra weight. This is wrapped with Kevlar, and then a superior e-glass cloth is used as the final surface prior to the gelcoat. Those areas that might come in contact with the ground are covered with a black urethane elastomer coating to further protect the lower surfaces. Although it looks like your standard gravel guard, this elastomer is very special. It was developed for use in Desert Storm to protect helicopter blades from abrasive sand storms and has about a 400 percent elongation factor, which means it will stretch considerably before it fails. As such, it is very resilient and is easily touched up.
The front splitters not only separate the airflow going under the car from the airflow going around the car, but they also generate significant downforce. To achieve this, the foam core is shaped to an inverse wing contour, which is then enveloped in the lay-up process with e-glass and Kevlar.
In many other kits, downforce will cause the splitter to distort and bend downward, increasing drag. The Greenwood splitter is unique inasmuch as the tendency to bend downward is controlled by a system of stops. A 6061 aircraft-grade aluminum bracket is attached to the upper frame, and an aircraft-grade cable, running through the brake duct, connects to the splitter, thereby limiting downward flex.
The side skirts incorporate a Z06 factory vent and ducting for rear-brake cooling. Buyers who already have a Z06 will maintain their existing ducting, while those with a coupe or convertible will benefit from this additional feature.
The rear tunnel comprises three pieces: the tunnel and two valance panels. Because the valance panels cover the mufflers, they are designed to leave an air gap of about 2 inches. The exhaust pipes are wrapped with an included header wrap to reduce the amount of heat they shed. Because the C5 Corvette also has its exhaust exiting at the center of the car, there is extra heat being vented through the tunnel, which helps to accelerate air flow. This has the effect of reducing drag and giving some additional downforce.
The wing, as with all the other pieces, is a composite of foam core, Kevlar, and fiberglass. The wing is manufactured in two halves, which are then bonded together. The legs are bonded separately, and these attach to the car's frame using two aircraft-grade 6061 aluminum girders. The main aluminum upright brackets are neatly machined and install through the license plate and taillight openings. The installation does not require the bumper to be removed and can be performed at home with basic tools and a drill.
There are two styles of wing: the "R" and the "RS." While both wings sit about 411/42 inches off the rear bumper, the R wing is wider and has winglets, allowing it to generate more downforce at lower speeds than the RS wing. The wing pictured is the R wing.
To be effective, rear-mounted wings must be in clean air so that the boundary layer flowing over the car body does not interfere with the low-pressure area generated below the wing. If the layers are too close together, there will be increased turbulence and drag, but no downforce. The Greenwood wing complies with aerodynamic theory.
The Greenwood kit reduces overall ground clearance to about 4 inches. This means that the splitter is already riding quite close to the ground for everyday street applications. Anyone preparing a car for competition might also lower the car using new springs and coilover shocks. This will lower the car even more and increase the ground plane effect. But, at this point, you will want to be very sure that you are only driving on smooth road surfaces.
NASCAR racer Geoff Bodine, who bought the first production kit, has provided a favorable review. Our own driver in the car also suggested that the increased downforce is real-it makes the car feel much more stable and connected to the ground. It also adds a certain responsiveness to steering inputs.
The Greenwoods are aware of how quickly their unique designs will be copied. This lesson was learned by their father through various deals with assorted merchandisers. To reduce the confusion between a real Greenwood part and a cheap knock-off, the boys have taken to serializing each ground effects package. A plate with a specific serial number is attached to the door jamb and is backed up by meticulous records and a certificate of authenticity.
Of course, many people will think about the aero package as just one element in a complete overhaul of their Corvette. However, the Greenwood aero package does not necessarily require any other specific modifications. You don't need bigger wheels or tires. You especially don't need to change the springs and shocks to lower the car. You don't need a bigger engine, either. According to Tim, once the kit is installed, what you really want is to have a proper alignment and then just drive the car. According to us, however, you will also want to have a very strong tolerance for other drivers crowding you to get a better look. This kit really makes the C5 stand out.